One means of inspecting work pieces for internal defects is to utilize an ultrasonic nondestructive testing system. In general these systems employ an electromechanical search unit which transmits ultrasonic energy or waves into the work piece or material under test. If there are internal discontinuities such as flaws or other defects within the material, portions of the ultrasonic energy reflect back to the search unit. The search unit produces an electrical signal representing the magnitude of the reflected ultrasonic energy.
The electrical signals representative of the received ultrasonic energy are typically displayed on a cathode ray tube oscilloscope. These display oscilloscopes are a cathode ray tube adapted specifically for ultrasonic material testing. These devices provide various visual displays representing any abnormalities in the received ultrasonic wave form. For example, in one type of display, a sweep signal synchronized with the pulsing of the transmitting search unit is applied to the horizontal deflection system of the oscilloscope. Electrical signals developed from the receiving search unit are applied to the vertical deflection system. This produces a visual representation of the ultrasonic discontinuities within the work piece. The presence of a defect within the material will appear as a pulse on the oscilloscope screen. The defect's location is indicated by the position of the pulse along the horizontal axis while its magnitude is represented on the vertical scale.
In addition to the cathode ray tube display, it is often desirable to provide a warning or alarm signal in response to detected defects which have magnitudes exceeding a critical level. It is known for example, to provide electrical circuit means for detecting electrical echo signals which exceed a predetermined threshold. The output of such detection circuits may be connected to turn an indicator light on or to sound an alarm.
These indicator or alarm lights are not, however, always seen by the operator who may be concentrating on manipulating the search unit about the surface of the test piece. Additionally, many search units are mounted in automated equipment in which a servo control mechanism moves the search unit along the work piece, freeing the operator to work on other projects. In such cases, the person monitoring the equipment may not see that the indicator light has come on. To provide a higher intensity indicator light is not always practical. Higher intensity warning lights consume a great deal of electrical power, and because the testing equipment is many times portable and battery operated, this of course is an undesirable if not impossible provision.